Michael Kjellman created CASSANDRA-14293:
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Summary: Speculative Retry Policy Should Support Specifying
MIN/MAX of 2 PERCENTILE and FIXED Policies
Key: CASSANDRA-14293
URL: https://issues.apache.org/jira/browse/CASSANDRA-14293
Project: Cassandra
Issue Type: Improvement
Reporter: Michael Kjellman
Assignee: Michael Kjellman
Currently the Speculative Retry Policy takes a single string as a parameter,
this can be NONE, ALWAYS, 99PERCENTILE (PERCENTILE), 50MS (CUSTOM).
The problem we have is when a single host goes into a bad state this drags up
the percentiles. This means if we are set to use p99 alone, we might not
speculate when we intended to to because the value at the specified percentile
has gone so high.
As a fix we need to have support for something like min(99percentile,50ms)
this means if the normal p99 for the table is <50ms, we will still speculate at
this value and not drag the happy path tail latencies up... but if the p99th
goes above what we know we should never exceed we use that instead.
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